This invention relates to methods for treating distillates obtained during the process of deodorizing various oils. More particularly, this invention relates to methods for recovering fatty acids, tocopherols, and sterols from a distillate obtained from the deodorizing of various oils.
Oils derived from plants and animals are valuable sources of fatty acids, tocopherols, and sterols. During the process of refining such oils, however, significant amounts of these components, especially the tocopherols and sterols, are lost to various intermediate byproducts and waste streams, which include acidulated soapstocks, deodorizer distillates, or both, depending on the refining method selected. Accordingly, numerous methods have been proposed for recovering fatty acids, tocopherols, and sterols from various refining intermediates, including deodorizer distillates that are obtained as byproducts of a high-temperature distillation step (commonly termed deodorization) during the production of oils and fats.
Deodorization is usually the final step in producing oils and fats from plant and animal sources. Vegetable oils such as soybean oil typically contain volatile impurities that can impart objectionable odor and taste. These volatile compounds generally must be removed to produce edible oils. Deodorization generally involves a steam stripping process wherein steam is contacted with oil in a distillation apparatus operating at low pressure and a temperature sufficient to vaporize objectionable volatile impurities at the operating pressure. This process, commonly known as vacuum-steam deodorization, relies upon volatility differences between the oil and the objectionable impurities to strip the relatively more volatile objectionable impurities from the relatively less volatile oil. In a typical vacuum-steam deodorizing process, vegetable oil is introduced into a distillation apparatus having a plurality of vertically spaced trays, commonly termed stripping trays. Within each stripping tray, steam injected into the vegetable oil entrains objectionable volatile impurities. The combined steam and entrained distillation vapors are usually collected and condensed to form a distillate that can be disposed of or processed further to recover valuable materials.
The major constituents of deodorizer distillates are fatty acids, tocopherols, and sterols, which are present in various relative amounts depending on the oil source and the refining steps the oil is subjected to prior to deodorization. Deodorizer distillate itself has a certain commercial value. However, greater value can be realized when deodorizer distillate is split into a fatty acid-enriched fraction and a fraction enriched in sterols and tocopherols.
Fatty acids isolated from deodorizer distillates are utilized in several nonfood applications and are particularly useful as fluidizing agents for lecithin. Such fatty acids also can be utilized as precursors in a wide variety of molecular synthesis schemes. Typically, the fatty acid portion of deodorizer distillate comprises C10-C22 saturated and unsaturated fatty acids. Soybean deodorizer distillate in particular contains about 50 percent by weight fatty acids.
Deodorizer distillates also contain sterols, which are valuable precursors in the production of hormones. Stigmasterol is used in manufacturing progesterone and corticoids. Sitosterol is used to produce estrogens, contraceptives, diuretics, and male hormones. Soybean deodorizer distillate in particular contains from about 10 to about 18 percent by weight total sterols, of which about 50% is sitosterol, about 20% is stigmasterol, about 20% is campesterol, and about 10% is other minor sterols.
The final major component of deodorizer distillates is tocopherol. Tocopherols are valuable natural antioxidants that help prevent oxidation and spoilage. Tocopherols are also utilized in the production of Vitamin E. Distillates obtained from soybean oil deodorization generally contain a mixture of xcex1, xcex2, xcex3, and xcex4 tocopherol isomers in a ratio of about 15:5:30:50. Alpha tocopherol has the most powerful biological Vitamin E activity. The other tocopherols have weaker Vitamin E activity but stronger antioxidant activity. If maximum Vitamin E activity is desired, non-alpha tocopherols can be converted into the alpha form by well-known techniques, such as methylation.
In the past, recovering tocopherols and sterols from deodorizer distillates and related mixtures has proved complicated and expensive. One difficulty associated with isolating one or more distillate fractions enriched in fatty acids, tocopherols, and/or sterols from deodorizer distillates is that the boiling points of sterols and tocopherols are roughly in the same range. Another difficulty is that deodorizer distillate can undergo thermal degradation if it is processed for extended periods at the temperatures at which sterols and tocopherols vaporize, such temperature conditions which can cause fatty acids to convert into undesirable trans isomeric forms.
Numerous methods have been proposed for treating deodorizer distillates to isolate and recover one or more components. In many of these methods, a first essential process step involves subjecting the fatty acids to an esterification or saponification reaction. For example, U.S. Pat. No. 3,153,055 teaches a process for isolating sterols and tocopherols from deodorizer distillate by esterifying the fatty acids with a monohydric alcohol under strongly acidic conditions. The sterols and tocopherols are then fractionally extracted from the esterification product mixture with a combination of polar and nonpolar solvents.
In an alternative esterification method, U.S. Pat. No. 5,487,817 teaches esterifying the sterols with the fatty acids and then distilling the resulting mixture to obtain a residue containing sterol esters and a distillate containing tocopherols. Sterols are then isolated from the residue by subjecting the sterol esters to cleavage under acidic conditions.
U.S. Pat. No. 2,349,270 discloses that deodorizer distillate can be treated with lime soap to saponify the fatty acids, followed by extraction of the unsaponifiable fraction (tocopherols and sterols) with acetone, in which the saponification products are insoluble. The extract is then washed and concentrated, as for example by solvent distillation, and then cooled to crystallize sterols which are removed by filtration, leaving a high purity tocopherol fraction. The fatty acid soaps formed by the process can be acidulated and converted into free fatty acids.
Extractive separation methods also have been employed in treating deodorizer distillates to isolate one or more components. For example, U.S. Pat. No. 5,138,075 describes a method for recovering tocopherols from a deodorized distillate which comprises contacting the distillate with liquid water at elevated temperature and pressure, thereby producing a raffinate phase stream having a relatively high concentration of tocopherols and an extract phase stream having a relatively high concentration of fatty acids. The raffinate stream and the extract stream are then cooled to a temperature at which the organic components thereof are immiscible with liquid water, whereupon removal of water produces a tocopherol-enriched fraction and a fatty acid-enriched fraction, respectively.
None of the above methods for isolating one or more components from a deodorizer distillate has proved satisfactory, however. Methods employing an esterification step or saponification step introduce processing complexity and require later processing steps that often involve use of strong mineral acids in order to convert the respective esters or soaps into free sterols and free fatty acids. Mineral acids can be dangerous in handling and can induce discoloration or other degradation of distillate components. Methods requiring extractive steps are expensive and create the potential for contamination by residual solvent.
Previously known methods for isolating one or more components from a deodorizer distillate generally have required lengthy and costly processing steps. Consequently, further improvements in methods for treating deodorizer distillates have been sought. The present invention relates to improved processes having advantages over those previously disclosed. The methods of the invention produce a fatty acid-enriched distillate fraction directly and simply from a vaporized distillate. The methods of the invention also produce a distillate fraction enriched in sterols and tocopherols, which can be treated further by various methods to isolate a sterol fraction and a tocopherol fraction.
One aspect of the present invention relates to methods for isolating one or more components from vaporized distillates obtained from the deodorization of various oils.
Another aspect of the present invention relates to methods for producing mixtures enriched in free fatty acids from distillates obtained from the deodorization of various oils.
Yet another aspect of the invention relates to methods for producing mixtures enriched in sterols and tocopherols from distillates obtained from the deodorization of various oils.
One embodiment of the invention is a process for isolating components from a vaporized distillate that comprises the steps of introducing a vaporized distillate comprising sterols, tocopherols, and fatty acids into a first condensing zone of a condensing unit having at least two condensing zones and operating at a pressure of less than about 10 mm Hg, the first condensing zone operating at a temperature of from about 330 to about 450xc2x0 F.; condensing a first fraction of the vaporized distillate in the first condensing zone to produce a first condensate enriched in sterols and tocopherols, leaving a remaining fraction of vaporized distillate; introducing the remaining fraction of vaporized distillate into a second condensing zone of the condensing unit, the second condensing zone operating at a temperature of from about 100 to about 170xc2x0 F.; and condensing a second fraction of the remaining fraction of vaporized distillate in the second condensing zone to produce a second condensate enriched in fatty acids, leaving a waste vapor.
Another embodiment of the invention is a process for isolating components from a vaporized distillate that comprises the steps of introducing a vaporized distillate comprising sterols, tocopherols, and fatty acids into a first condensing zone of a condensing unit having at least two condensing zones and operating at a pressure of less than about 10 mm Hg, the first condensing zone operating at a temperature of from about 330 to about 450xc2x0 F.; condensing a first fraction of the vaporized distillate in the first condensing zone to produce a first condensate enriched in sterols and tocopherols, leaving a remaining fraction of vaporized distillate; introducing the remaining fraction of vaporized distillate into a second condensing zone of the condensing unit, the second condensing zone operating at a temperature of from about 100 to about 170xc2x0 F.; condensing a second fraction of the remaining fraction of vaporized distillate in the second condensing zone to produce a second condensate enriched in fatty acids, leaving a waste vapor; recovering the first condensate; and recovering the second condensate.
Yet another embodiment of the invention is a process for isolating components from a vaporized distillate that comprises the steps of introducing a vaporized distillate comprising sterols, tocopherols, and fatty acids into a first condensing zone of a condensing unit having at least two condensing zones and operating at a pressure of less than about 10 mm Hg, the first condensing zone operating at a temperature of from about 330 to about 450xc2x0 F.; condensing a first fraction of the vaporized distillate in the first condensing zone to produce a first condensate enriched in sterols and tocopherols by passing the vaporized distillate through a first packing where it is contacted with recycled first condensate maintained at a temperature of about 380xc2x0 F., leaving a remaining fraction of vaporized distillate; introducing the remaining fraction of vaporized distillate into a second condensing zone of the condensing unit, the second condensing zone operating at a temperature of from about 100 to about 170xc2x0 F.; and condensing a second fraction of the remaining fraction of vaporized distillate in the second condensing zone to produce a second condensate enriched in fatty acids by passing the remaining fraction of vaporized distillate through a second packing where it is contacted with recycled second condensate maintained at a temperature of about 135xc2x0 F., leaving a waste vapor.
A further embodiment of the invention is a process for isolating components from a vaporized distillate that comprises the steps of introducing a vaporized distillate comprising sterols, tocopherols, and fatty acids into a first condensing zone of a condensing unit having at least two condensing zones and operating at a pressure of less than about 10 mm Hg, the first condensing zone operating at a temperature of from about 330 to about 450xc2x0 F.; condensing a first fraction of the vaporized distillate in the first condensing zone to form a first condensate enriched in sterols and tocopherols by passing the vaporized distillate through a first packing where it is contacted with recycled first condensate maintained at a temperature of about 380xc2x0 F., leaving a remaining fraction of vaporized distillate; introducing the remaining fraction of vaporized distillate into a second condensing zone of the condensing unit, the second condensing zone operating at a temperature of from about 100 to about 170xc2x0 F.; condensing a second fraction of the remaining fraction of vaporized distillate in the second condensing zone to produce a second condensate enriched in fatty acids by passing the remaining fraction of vaporized distillate through a second packing where it is contacted with recycled second condensate maintained at a temperature of about 135xc2x0 F., leaving a waste vapor; recovering the first condensate; and recovering the second condensate.
These and other aspects of the invention will become apparent in light of the detailed description below.